One of the most fascinating predictions of Einstein’s General Theory of Relativity is that light does not travel in a perfectly straight line when it passes near a massive object. Instead, gravity causes space-time itself to curve, and light follows the curvature of this space-time—appearing to bend.
This effect, known as gravitational lensing, was first confirmed in 1919 when astronomers observed that the position of stars near the Sun appeared shifted during a total solar eclipse. The starlight was bent as it passed through the Sun’s gravitational field, providing the first major experimental support for Einstein’s theory.
Unlike Newtonian gravity, which treats gravity as a force acting at a distance, general relativity describes gravity as the warping of space and time by mass and energy. Photons, although massless, are affected by this curvature because they move along the straightest possible path in curved space—called a geodesic.
Gravitational lensing has become a powerful tool in astronomy and cosmology. It allows scientists to:
- Detect dark matter (by how it distorts the light of background galaxies),
- Observe distant galaxies and quasars,
- Study the expansion of the universe.
Thus, the bending of light by gravity is a dramatic demonstration of how mass can influence the path of light and a cornerstone of modern gravitational physics.